CO gas-discharge lasers with average output power greater than 250 Watts (W) have recently become commercially available. Such lasers have been accepted as advantageous for certain laser-machining operations, particularly laser-drilling of via-holes in printed circuit boards PCBs.
Via-hole drilling using a pulsed CO laser is described in detail in U.S Pre-grant Publication No. 2015/0083698, assigned to the assignee of the present invention, and the complete disclosure of which is hereby incorporated herein by reference. In this method, pulses from a CO laser are temporally shaped by removing leading and trailing edges of the pulse with slow rise and fall times. An acousto-optic modulator (AOM) is used for this operation. The AOM is operated to pass the unwanted leading and trailing edges of pulse directly with the AOM turned “off”, and to diffract a wanted, temporally shaped portion, of the pulse along a path to the workpiece (PCB). Means are provided for compensating for spectral (chromatic) dispersion introduced into the temporally shaped pulse by the diffraction of the AOM.
In preferred embodiments of the above referenced via-hole drilling operation, the drilling is performed on one workpiece at a time. Operational productivity could be increased by adapting the method for operating on two or more workpieces at a time.